Characterizing pore size distribution of high maturity shales and main controlling factors analysis: A case study of Permian Gufeng Formation in the Lower Yangtze region, China

Shale gas resource is heterogeneously distributed in Permian Gufeng Formation in the Xuancheng area, Anhui Province. This research aims to investigate the pore size distribution of the Permian Gufeng shales via 16 core samples analyses, combined with x-ray diffraction, low-pressure nitrogen gas adsorption (N-2-GA), CO2 gas adsorption (CO2-GA) and scanning electron microscopy (SEM). N-2-GA shows that the nanopores (diameter < 10 nm) are dominated and developed in the samples. The Brunauer-Emmett-Teller (BET) specific surface area (SSA) of the samples ranges from 6.7051 to 29.4384 m(2)/g, with a mean of 16.0931 m(2)/g. CO2-GA results illustrate that micropore is well developed, especially the pores with a diameter of 0.5-0.6 and 0.8 nm. The total organic carbon (TOC) content of the Gufeng shale ranges from 0.42% to 12.82% with an average content of 6.44%, which has both positive correlation with pore SSA and pore volume, while carbonate mineral content has a positive correlation with pore SSA and the volume of macropore and mesopore. Clay mineral content is a negative correlation with pore SSA and micropore volume. Therefore, the high-maturity Permian Gufeng shale could be more preferential high-quality gas shale reservoir for further exploration and development in the Xuancheng area, which has more than 4% TOC content, relatively higher carbonate mineral content and relatively lower clay mineral content.